Silicone project; Bubbles in a Dragonskin cast?

So I have found bubbles in a tongue I cast last night for practice. It was cast in Dragonskin 10 ';medium'  I used a dye purchased from BITY,

http://www.shop.brickintheyard.com/Silicone-Pigment-1oz-SiPi.htm


Just wondering if a vacuum chamber is vital/absolute needed in this case? Or can I cast dragonskin without one?